NATURAL AND ARTIFICIAL INCUBATION 



87 



this purpose. Most incubators come equipped with testing 

 chimneys that fit on an incubator lamp. An electric light 

 or a kerosene lamp may be used in a box with a hole 

 slightly smaller than an egg cut in the side of the box and 

 at the same level as the light. 

 A hole slightly larger than 

 the chimney of the lamp 

 should be cut in the top of the 

 box to allow the heat to es- 

 cape. (See Figure 86.) 



The eggs, when tested, 

 should be held with the large 

 end up so that the size of the 

 air cell may be seen as well as 

 the condition of the embryo. 

 The testing should take 

 place in a darkened room. 

 The infertile egg when held be- 

 fore the hole of the tester will 

 look perfectly clear, or the 

 same as a fresh egg. 



A fertile egg will show a 

 small dark spot, known as the 

 embryo, with a mass of little 

 blood veins radiating in all 

 directions, if the embryo is 

 living. 



If the germ of the egg is 

 dead and it has been incubated for at le.ast 46 hours, the 

 blood settles away from the embryo toward the edge of the 

 yolk, usually forming an irregular circle of blood, known 

 as a blood ring. All infertile and dead-germ eggs should 

 be removed at the first test. 



Eggs containing living embryos are dark and well filled 



Figure 85. — The eggs should be tested 

 at least twice during the period of 

 incubation, preferably on the 7th 

 and 14th days, and all infertile eggs 

 and those with dead germs removed. 



